Piezoelectric devices are known and are in use in a variety of applications. Typically, such devices include piezoelectric material layers (e.g., a lead zirconate titanate (PZT) layer) integrated with silicon-based semiconductors and such hybrid structures are used for applications such as micro-electro-mechanical-systems (MEMS) sensors and actuators, surface acoustic wave (SAW) devices and non-volatile memory devices. However, silicon-based devices have limitations such as ambient temperature operation and other issues like interface diffusion between an insulator and the silicon substrate and formation of natural silicon oxide layer.
Certain piezoelectric devices employ diamond substrates that have relatively higher thermal conductivity, large band gap and higher resistivity as compared to the silicon-based devices. Moreover, diamond has substantially high acoustic wave velocity and integration of diamond substrate with piezoelectric material layer provides an opportunity to fabricate SAW devices that may be used for high frequency applications.
Unfortunately, it is difficult to deposit a piezoelectric material layer on the diamond substrate without use of a buffer layer such as platinum or strontium titanate due to thermal expansion mismatch between the piezoelectric material layer such as PZT layer and diamond substrate. In particular, it is difficult to form perovskite phase PZT layer on a diamond substrate. Typically, formation of pyrochlore PZT is the predominant phase in the PZT layers deposited directly diamond substrate. However, pyrochlore PZT does not exhibit piezoelectric or ferroelectric properties thereby rendering them unsuitable for device fabrication.